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Craig A Grimes – One of the best experts on this subject based on the ideXlab platform.
self assembled tio2 nanotube arrays by Anodization of titanium in diethylene glycol approach to extended pore wideningLangmuir, 2010Co-Authors: Sorachon Yoriya, Craig A GrimesAbstract:
We report on the formation of titanium dioxide nanotube arrays having the largest known pore size, approximately 350 nm diameter. The nanotube arrays are synthesized by Ti foil Anodization in a diethylene glycol electrolyte containing low (0.5−2%) concentrations of hydrofluoric acid. The large pore size nanotube arrays are achieved with extended Anodization durations of approximately 120 h, with the Anodization duration showing a more significant effect on pore diameter than the Anodization voltage. It appears that the combined effects of hydrofluoric acid content and Anodization duration determine the lateral etching rate of the nanotubes, leading to the larger pore size nanotubes.
synthesis of ordered arrays of discrete partially crystalline titania nanotubes by ti Anodization using diethylene glycol electrolytesJournal of Materials Chemistry, 2008Co-Authors: Sorachon Yoriya, Sanjeev Sharma, Craig A GrimesAbstract:
We report the fabrication of self-organized titania nanotube arrays comprised of separated, discrete nanotubes by Ti Anodization in fluoride ion containing diethylene glycol (DEG) electrolytes. We describe the effect of the fluoride bearing species used in the Anodization electrolyte on the tube morphology, degree of tube-to-tube separation, and crystallization. The arrayed nanotubes achieved from DEG electrolytes containing either HF or NH4F are fully separated with open pores.
photoelectrochemical and water photoelectrolysis properties of ordered tio2 nanotubes fabricated by ti Anodization in fluoride free hcl electrolytesJournal of Materials Chemistry, 2008Co-Authors: Nageh K Allam, Karthik Shankar, Craig A GrimesAbstract:
Described is the synthesis of TiO2 nanotube array films by Anodization of Ti foil in HCl electrolytes containing different H2O2 concentrations. Highly ordered nanotube arrays up to 860 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained for one hour Anodizations using a 0.5 M HCl aqueous electrolyte containing 0.1–0.5 M H2O2 concentrations for Anodization potentials between 10–23 V. The use of ethylene glycol as the electrolyte medium significantly alters the Anodization kinetics and resulting film morphologies; nanotube bundles several microns in length achieved for Anodization potentials between 8 V and 18 V in only a few minutes. The nanotube arrays obtained from the ethylene glycol electrolytes show relatively higher photocurrents, ≈0.8 mA cm−2 under AM 1.5. Under 100 mW cm−2 AM 1.5 illumination a 500 °C annealed 1 cm2 nanotube array sample, obtained by Anodization of a Ti foil sample in ethylene glycol + 0.5 M HCl + 0.4 M H2O2 electrolyte, demonstrates a hydrogen evolution rate of approximately 391 μL h−1 by water photoelectrolysis, time-power normalized evolution rate of 3.9 mL W−1 h−1, with water splitting confirmed by the 2 : 1 ratio of evolved hydrogen to oxygen.
Ulrich Gösele – One of the best experts on this subject based on the ideXlab platform.
self ordered anodic aluminum oxide formed by h2so4 hard AnodizationACS Nano, 2008Co-Authors: Kathrin Schwirn, Martin Steinhart, Kornelius Nielsch, R Hillebrand, Ulrich GöseleAbstract:
The self-ordering of nanoporous anodic aluminum oxide (AAO) in the course of the hard Anodization (HA) of aluminum in sulfuric acid (H2SO4) solutions at Anodization voltages ranging from 27 to 80 V was investigated. Direct H2SO4-HA yielded AAOs with hexagonal pore arrays having interpore distances Dint ranging from 72 to 145 nm. However, the AAOs were mechanically unstable and cracks formed along the cell boundaries. Therefore, we modified the Anodization procedure previously employed for oxalic acid HA (H2C2O4-HA) to suppress the development of cracks and to fabricate mechanically robust AAO films with Dint values ranging from 78 to 114 nm. Image analyses based on scanning electron micrographs revealed that at a given Anodization voltage the self-ordering of nanopores as well as Dint depend on the current density (i.e., the electric field strength at the bottoms of the pores). Moreover, periodic oscillations of the pore diameter formed at Anodization voltages in the range from 27 to 32 V, which are remin…
Structural engineering of nanoporous anodic aluminium oxide by pulse Anodization of aluminium.Nature nanotechnology, 2008Co-Authors: Woo K. Lee, Woo Lee, Kathrin Schwirn, Martin Steinhart, Eckhard Pippel, Roland Scholz, Ulrich Goesele, Ulrich GöseleAbstract:
Nanoporous anodic aluminium oxide has traditionally been made in one of two ways: mild Anodization or hard Anodization. The first method produces self-ordered pore structures, but it is slow and only works for a narrow range of processing conditions; the second method, which is widely used in the aluminium industry, is faster, but it produces films with disordered pore structures. Here we report a novel approach termed “pulse Anodization” that combines the advantages of the mild and hard Anodization processes. By designing the pulse sequences it is possible to control both the composition and pore structure of the anodic aluminium oxide films while maintaining high throughput. We use pulse Anodization to delaminate a single as-prepared anodic film into a stack of well-defined nanoporous alumina membrane sheets, and also to fabricate novel three-dimensional nanostructures.
self ordering behavior of nanoporous anodic aluminum oxide aao in malonic acid AnodizationNanotechnology, 2007Co-Authors: Woo Lee, Kornelius Nielsch, Ulrich GöseleAbstract:
The self-ordering behavior of anodic aluminum oxide (AAO) has been investigated for Anodization of aluminum in malonic acid (H4C3O4) solution. In the present study it is found that a porous oxide layer formed on the surface of aluminum can effectively suppress catastrophic local events (such as breakdown of the oxide film and plastic deformation of the aluminum substrate), and enables stable fast anodic oxidation under a high electric field of 110‐140 V and ∼100 mA cm −2 . Studies on the self-ordering behavior of AAO indicated that the cell homogeneity of AAO increases dramatically as the Anodization voltage gets higher than 120 V. Highly ordered AAO with a hexagonal arrangement of the nanopores could be obtained in a voltage range 125‐140 V. The current density (i.e., the electric field strength (E) at the bottom of a pore) is an important parameter governing the self-ordering of the nanopores as well as the interpore distance (Dint) for a given Anodization potential (U ) during malonic acid Anodization. S Supplementary data are available from stacks.iop.org/Nano/18/475713 (Some figures in this article are in colour only in the electronic version)
Kourosh Kalantarzadeh – One of the best experts on this subject based on the ideXlab platform.
Anodization of ti thin film deposited on itoLangmuir, 2009Co-Authors: A Z Sadek, Haidong Zheng, Kay Latham, W Wlodarski, Kourosh KalantarzadehAbstract:
We have investigated several key aspects for the self-organization of nanotubes in RF sputtered titanium (Ti) thin films formed by the Anodization process in fluoride-ion-containing neutral electrolytes. Ti films were deposited on indium tin oxide (ITO) glass substrates at room temperature and 300 °C, and then anodized. The films were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV−vis spectrometry before and after Anodization. It was observed that Anodization of high temperature deposited films resulted in nanotube type structures with diameters in the range of 10−45 nm for an applied voltage of 5−20 V. In addition, the anatase form of TiO2 is formed during the Anodization process which is also confirmed using photocurrent measurements. However, the Anodization of room temperature deposited Ti films resulted in irregular pores or holes.
fabrication of nanostructured tio2 by Anodization a comparison between electrolytes and substratesSensors and Actuators B-chemical, 2008Co-Authors: W Wlodarski, Sasikaran Kandasamy, Kourosh KalantarzadehAbstract:
Nanostructured TiO2 thin films with large surface to volume ratio are fabricated from titanium thin films deposited on various substrates employing an Anodization technique. The effect of the electrolytes (e.g. HF-containing electrolyte or neutral electrolyte) and substrates (e.g. silicon substrate or silicon carbide substrate) on the microstructure of the anodized thin films are investigated. Nanoporous films on silicon substrates with an average pore diameter of 25 nm and interpore distance of 40 nm are obtained by anodizing in an aqueous HF electrolyte solution after a comprehensive investigation of the Anodization conditions. When the Anodization is performed in a neutral electrolyte without HF solution, discrete nanotubular thin films are formed. The anodic film on silicon carbide substrate shows a quite different morphology, which exhibits a layered structure after Anodization. The nanostructured TiO2 films are characterized using SEM and XRD techniques and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different nanostructures.
formation of nanoporous titanium oxide films on silicon substrates using an Anodization processNanotechnology, 2006Co-Authors: Qunbao Yang, Nanfei Zhu, Kourosh KalantarzadehAbstract:
The formation of nanoporous TiO2 by Anodization of titanium films deposited on silicon substrates was investigated. Films with homogeneously distributed pores having an average pore diameter of 25 nm and interpore distance of 40 nm were obtained by Anodization in an aqueous HF electrolyte solution after a comprehensive investigation of the Anodization conditions. It was shown that the magnitude of the Anodization current and voltage have significant roles in the formation of different surface morphologies with different pore dimensions, ranging from big pits to nanosize porous structures. The study showed that the nanoporous structure is formed only in 0.5–1.0 wt% HF solution while keeping the anodizing potential at 3–5 V. The porous TiO2 films were characterized using scanning electron microscopy and x-ray diffraction techniques, and their formation conditions are discussed. In addition, a growth mechanism model is presented to explain the formation of different surface structures.